This invention relates to the setting of the tooth trace of helical gears in an infinitely variable transmission.
Tokkai 2000-213623 published by the Japanese Patent Office in 2000 discloses an infinitely variable transmission (IVT) for a vehicle which combines a fixed speed ratio transmission, a continuously variable transmission (CVT) and a planetary gear set.
In this IVT, the output of the CVT is transmitted to a sun gear which is fixed to a central shaft of the planetary gear set through a chain. The output of the fixed speed ratio transmission is transmitted to the planet carrier of the planetary gear set. The ring gear of the planetary gear set is fixed to the output shaft of the IVT which is supported on an outer periphery of the central shaft. The planetary gear set varies the speed and direction of rotation of the ring gear in response to the difference between the rotation speed of the planet carrier and the sun gear and transmits torque to the drive shaft of the vehicle through an IVT output gear which is fixed on the output shaft.
A low-noise helical gear is used on the IVT output gear and in the fixed speed ratio transmission. The tooth trace of these helical gears is set to eliminate the bending moment applied on the central shaft by the tension of the chain.
Tokkai Hei 11-63139 published by the Japanese Patent Office in 1999 discloses an IVT which transmits the output of the CVT to the sun gear of the planetary gear set by combining two helical gears without the use of a chain. The two helical gears transmit rotations in an opposite direction to the direction of rotation of the chain. As a result, the direction of rotation of the sun gear is opposite to the direction of rotation of the sun gear in the IVT disclosed in Tokkai 2000-213623. In this IVT, the direction of rotation of the sun gear and the planet carrier are arranged to reverse the direction of the output rotations of the fixed speed ratio transmission using a counter gear.
Since this IVT transmits the CVT output to the sun gear using a helical gear, the application of a bending moment on the central shaft differs from the IVT disclosed in Tokkai 2000-213623.
It is therefore an object of this invention to reduce the bending moment applied to the output shaft in an IVT in which the CVT output is transmitted to the planetary gear via helical gears.
In order to achieve the above object, this invention provides a special arrangement of an infinitely variable transmission comprising an input shaft, a continuously variable transmission which outputs a rotation of the input shaft to a first helical gear at an arbitrary speed ratio, a fixed speed ratio transmission which outputs a rotation of the input shaft to a second helical gear at a fixed speed ratio, and a third helical gear which changes a rotation direction and a rotation speed according to a difference between a rotation speed of the first helical gear and a rotation speed of the second helical gear.
In this infinitely variable transmission, the first helical gear, the second helical gear and the third helical gear are supported on a common rotation shaft such that one of the first helical gear, the second helical gear and the third helical gear is disposed between the other two gears. One of the other two gears has a tooth trace which generates a thrust force exerting a bending moment on the rotation shaft in a direction opposite to a direction of a bending moment exerted by a radial force acting on the gear which is disposed between the other two gears on the rotation shaft.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.